This invention relates generally to marine drive apparatuses and more specifically to such apparatuses having means for vertically adjusting the operating position of a stern-drive propeller.
Various apparatuses for driving one or more stern-drive boat propellers are known in the art. Probably the most common system includes an engine and a transmission located inside a boat hull. Power is communicated to a propeller via a propeller shaft connected between the transmission and the propeller and passing through a notch transom via a watertight fitting. Also known are inboard-outboard devices that have inboard engines coupled to steerable out-drives. Some of the latter systems have transmissions mounted within the hull, and some have transmissions mounted within the out-drive.
A planing boat has specific power application requirements related to the fact that, at planing speed, a component of the force of the water acting on the hull causes it to lift so that only a rear portion of the boat is in contact with the water. A benefit of reduced hull-water contact is reduced drag, which translates into increased boat speed at a given power setting. Drag can be further lessened by maintaining a minimum angle between respective hull and water surfaces.
The angle the hull lower surface makes with the water surface at planing speed is related to the location of the propeller. The force of a propeller located well below the bottom of the boat generates a relatively large moment that tends to lift the bow of the boat and to reduce the effectiveness of the planing characteristics of the hull.
The angle the hull lower surface makes with the water surface at planing speed is also related to the angle between the axis of rotation of the propeller and the surface of the water. The greater the angle is between the propeller shaft and the water surface, the greater will be a moment generated by the force of the propeller that tends to depress the bow. Since the plane of rotation of each propeller is at right angles to its associated propeller shaft, an angle between the propeller shaft and the water surface is reflected in an equal angle between the propeller plane and the vertical. This places downwardly moving propeller blades at a somewhat greater pitch than upwardly moving blades relative to water flow, which reduces propeller efficiency and promotes vibration.
An improvement in drive efficiency would be effected if the drive components could be disposed so that drive force is aligned with the bottom surface of the hull. Even this would not provide an ideal solution, however, because such factors as changing boat load distribution, water surface conditions and wind velocity contribute to unstable trim symmetry.
An object of the present invention is to provide an improved marine drive apparatus for a boat wherein the operating position of a drive propeller is vertically adjustable.
Another object is to provide a marine drive apparatus that is capable of directing its thrust substantially along the plane of the lower surface of a planing boat hull.
Yet another object is to provide a marine drive apparatus having a decreased angle between the rotation axis of the propeller and the plane of the lower surface of the planing boat hull without increasing the number of friction-generating drive displacement elements.
Still another object is to provide a marine drive apparatus wherein a substantial portion thereof is above the water when the boat is running at planing speed.
Another object is to provide a marine drive apparatus, the drive thrust of which is received by an inboard universal joint between a propeller shaft and a transmission output member, rather than by a through-hull fitting in a transom.
A feature of the present invention is a pivot arm assembly that supports a propeller shaft and responds to mechanical input from a trim drive to adjust the vertical position of the propeller shaft.
Another feature is mounting the trimmable marine drive apparatus in a notch disposed at the stern of a boat so that the direction of propeller thrust is in the plane of the hull lower surface when the boat is running at planing speed.
Still another feature is that the propeller shaft is maintained at a small angle relative to the water surface and that the plane of the propeller is thus maintained at a small angle relative to the vertical.
Yet another feature is that most of the trimmable marine drive apparatus is located above the surface of the water when the boat is running at planing speed.
Another feature is a fin depending from the shaft support to increase stability and to reduce the likelihood of striking submerged objects with the propeller, rudder or shaft support when the boat is in motion.
An advantage of the present invention is that the capability of adjusting the vertical position of the propeller provides means for maximizing trim efficiency and boat performance.
Another advantage is that maintaining the propeller shaft at a small angle relative to the water surface and the axis of rotation of the propeller generally in line with the lower surface of the hull reduces bow-lifting and bow-depressing moments, thus reducing hull drag and wind influences on the hull.
Still another advantage is that maintaining the plane of the propeller nearly vertical maximizes propeller efficiency and minimizes propeller vibration caused by pitch differences between ascending and descending propeller blades.
Yet another advantage is gained by the notch mounting position and the pivot arm assembly design in that having most of the trimmable marine drive apparatus above the water surface when the boat is running at planing speed reduces drive apparatus drag, thus increasing boat performance.
Another advantage gained by the notch mounting position and the pivot arm assembly design is that a minimum number of friction-generating and drag-generating drive displacement components are required to position the axis of rotation of the propeller proximate the water surface when the boat is running at planing speed.
Other advantages gained by the notch mounting position and the pivot arm assembly design include an increased stabilization and a decreased likelihood of striking submerged objects with the propeller, rudder or shaft support when the boat is in motion.
In realizing the aforementioned and other objects, features and advantages, the trimmable marine drive apparatus of the present invention includes, for use with a power boat having a planing hull with a notch and having an inboard drive assembly, which includes an engine and a transmission operably connected thereto, a propeller shaft having a driven end pivotally connected to and rotatably driven by the transmission, a driving end opposite the driven end, and a central longitudinal axis of rotation.
A propeller is secured to the driving end of the propeller shaft. The propeller is preferably a surfacing-type propeller designed to run efficiently while only partially submerged. The driven end of the propeller shaft is pivotally connected to the transmission with a universal joint. The universal joint compensates for angular adjustments to the propeller shaft and receives the drive thrust generated by the propeller.
The drive apparatus further includes a pivot arm assembly having a pivot arm including a forward end pivotally attached to the hull within the notch for movement about a transverse axis. The pivot arm also has a rear end rearwardly spaced from the forward end, a shaft support rotatably supporting the propeller shaft proximate its driving end, and a strut connecting the shaft support to the pivot arm.
The shaft support includes an upper portion and a lower portion connected thereto. Each portion is configured to provide in cooperation a generally longitudinal passage through the shaft support. A sheave-shaped pivot bearing is rotatably disposed within the longitudinal passage, and each of the upper and lower portions of the shaft support are further configured to conform to the external contours of the pivot bearing. This limits motion thereof to angular displacement in a vertical plane.
A bearing sleeve is positioned within a portion of the longitudinal passage of the shaft support to rotatably support the propeller shaft. The bearing sleeve resides within a diametrically aligned aperture in the pivot bearing. The longitudinal passage is vertically elongated to accommodate angular displacements, in a vertical plane, of the bearing sleeve and the propeller shaft when the trim drive is operated. A fin depends from the underside of the shaft support.
A trim drive is mounted within the hull and has an extendable member depending through the hull and pivotally connected to the pivot arm to raise and lower the rear end thereof. Vertical adjustments of the pivot arm by the trim drive are communicated to the propeller via the strut, the shaft support and the propeller shaft to maximize boat performance under various operating conditions. The trim drive is hydraulically operated and is capable of angularly positioning the propeller shaft within a range of at least three degrees above and below an angle that vertically positions the axis of rotation of the propeller shaft at the propeller in the same plane as that of the planing hull at the notch transom.